Images of Exoplanetary Journeys

by Paul Gilster on November 30, 2012

Stretch out your time horizons and interstellar travel gets a bit easier. If 4.3 light years seems too immense a distance to reach Alpha Centauri, we can wait about 28,000 years, when the distance between us will have closed to 3.2 light years. As it turns out, Alpha Centauri is moving in a galactic orbit far different from the Sun’s. As we weave through the Milky Way in coming millennia, we’re in the midst of a close pass from a stellar system that will never be this close again. A few million years ago Alpha Centauri would not have been visible to the naked eye.

The great galactic pinball machine is in constant motion. Epsilon Indi, a slightly orange star about an eighth as luminous as the Sun and orbited by a pair of brown dwarfs, is currently 11.8 light years out, but it’s moving 90 kilometers per second relative to the Sun. In about 17,000 years, it will close to 10.6 light years before beginning to recede. Project Ozma target Tau Ceti, now 11.9 light years from our system, has a highly eccentric galactic orbit that, on its current inbound leg, will take it to within the same 10.6 light years if we can wait the necessary 43,000 years.

And here’s an interesting one I almost forgot to list, though its close pass may be the most intriguing of all. Gliese 710 is currently 64 light years away in the constellation Serpens. We have to wait a bit on this one, but the orange star, now at magnitude 9.7, will in 1.4 million years move within 50,000 AU of the Sun. That puts it close enough that it should interact with the Oort Cloud, perhaps perturbing comets there or sending comets from its own cometary cloud into our system. In any case, what a close-in target for future interstellar explorers!

I’m pulling all this from Erik Anderson’s new book Vistas of Many Worlds, whose subtitle — ‘A Journey Through Space and Time’ — is a bit deceptive, for the book actually contains four journeys. The first takes us on a tour of ten stars within 20 light years of the Sun, with full-page artwork on every other page and finder charts that diagram the stars in each illustration. The second tour moves through time and traces the stars of an evolving Earth through text and images. Itinerary three is a montage of scenes from known exoplanets, while the fourth tour takes us through a sequence of young Earth-like worlds as they develop.

Anderson’s text is absorbing — he’s a good writer with a knack for hitting the right note — but the artwork steals the show on many of these pages, for he’s been meticulous at recreating the sky as it would appear from other star systems. It becomes easy to track the Sun against the background of alien constellations. Thus a spectacular view of the pulsar planet PSR B1257+12 C shows our Sun lost among the brighter stars Canopus and Spica, with Rigel and Betelgeuse also prominent. The gorgeous sky above an icy ocean on a planet circling Delta Pavonis shows the Sun between Alpha Centauri and Eta Cassiopeiae. Stellar motion over time and the perspectives thus created from worlds much like our own are a major theme of this book.

From Epsilon Eridani, as seen in the image below, the Sun is a bright orb seen through the protoplanetary disk at about the 4 o’clock position below the bright central star.

Image: The nearby orange dwarf star Epsilon Eridani reveals its circumstellar debris disks in this close-up perspective. Epsilon Eridani is only several hundred million years old and perhaps resembles the state of our own solar system during its early, formative years. Credit: Erik Anderson.

Vistas of Many Worlds assumes a basic background in astronomical concepts, but I think even younger readers will be caught up in the wonder of imagined scenes around planets we’re now discovering, which is why I’m buying a copy for my star-crazed grandson for Christmas. He’ll enjoy the movement through time as well as space. In one memorable scene, Anderson depicts a flock of ancient birds flying through a mountain pass 4.8 million years ago. At that time, the star Theta Columbae, today 720 light years away, was just seven light years out, outshining Venus and dominating the sunset skies of Anderson’s imagined landscape.

And what mysteries does the future hold? The end of the interglacial period is depicted in a scene Anderson sets 50,000 years from now, showing a futuristic observation station on the west coast of an ice-choked Canada. The frigid landscape and starfield above set the author speculating on how our descendants will see their options:

Will the inhabitants of a re-glaciating Earth seek refuge elsewhere? Alpha Centauri, our nearest celestial neighbor, has in all this time migrated out of the southern skies to the celestial equator, where it can be sighted from locations throughout the entire globe. It seems to beckon humanity to the stars.

And there, tagged by the star-finder chart and brightly shining on the facing image, is the Alpha Centauri system, now moving inexorably farther from our Sun but still a major marker in the night sky. Planet hunter Greg Laughlin has often commented on how satisfying it is that we have this intriguing stellar duo with accompanying red dwarf so relatively near to us as we begin the great exoplanet detection effort. We’re beginning to answer the question of planets around Alpha Centauri, though much work lies ahead. Perhaps some of that work will be accomplished by scientists who, in their younger years, were energized by the text and images of books like this one.



Aleksandar November 30, 2012 at 11:22

I find it odd that this aspect is rarely mentioned when discussing interstellar journeys. For example, you might read that one of the Voyagers would need 40 000 years to reach the nearest star, even if it was aimed at it (which it is not). Now, aiming it might be a little bit complicated, but nobody mentions this. You would need to navigate, taking into account the stellar motions over a period of 40 000 years, and with no fuel for trajectory corrections…

Greg November 30, 2012 at 14:13

” In any case, what a close-in target for future interstellar explorers!”

I’m really hoping that in 1.4 Million years we’ve been going to the stars on a routine bases.

Stan Clark November 30, 2012 at 15:22

Ok we can forward predict what stars will be close to us in the future, so which star was closest to us during the Late Heavy Bombardment and how close? With Gliese 710 being within 50,000 AU of us in 1.4 Million years and disturbing the Oort Cloud are we due for another Heavy Bombardment?

Enzo November 30, 2012 at 17:22

The astrometric ESA mission Gaia is supposed to measure not only the position, but at least the radial velocity of 1 billion stars. Not sure about the real velocity but I guess that, for nearby stars, that might be possible with astrometric methods from Gaia’s data. It will then be possible to know pretty clearly what’s going to happen in the next few million years and what has happened in the last few.

On a different topic, the confirmation of ice on the poles of Mercury makes one hope that something similar might be happening on some of the terrestrial planets in the newly discovered compact systems.

Wojciech J November 30, 2012 at 20:33

If you want to get a nice glimpse of views from other worlds including the sky I recommend Space Engine, its a free program for simulating known and generated star systems and large portion of observable universe. It’s quite good.

Erik Anderson November 30, 2012 at 22:16

@ Paul : Thank you so much for featuring my book on Centauri Dreams!

@ Aleksander: I too am amused by statements certifying when spacecraft escaping the Solar System will reach such-and-such a star, knowing that many stars have heliocentric velocities that are even faster that the spacecraft! But it’s not odd — a truer account of stellar encounters requires that one bothers with the kind of detailed information available, e.g., in my XHIP database (see the “Data” page on my astrostudio website). If anyone can direct me to EXACT information about the escape trajectories of Pioneers 10 & 11 and Voyagers 1 & 2, I could (for fun!) report flyby projections for these spacecraft over the next few million years.

@ Stan: The Late Heavy Bombardment was billions of years and several Galactic orbits ago! It’s simply not possible to project anything ~that~ far back in time. However, the Sun may have still been contained by its birth cluster during that primordial epoch and encounters with high-mass siblings were eminently probable. One wonders what the fate of the Earth would be if the Sun lingered in its birth cluster for too long; I discuss this matter on page 100 of Vistas.

@ Enzo: I talk about Gaia with great enthusiasm on page 118 of Vistas, juxtaposed with a portrayal of the spacecraft on the launchpad late in 2013! Gaia will find many low mass stars (e.g. red dwarfs) that have closely encountered /will closely encounter the Solar System in a +/- few-million-year time-frame but were overlooked by Hipparcos because of Hipparcos’ shallower magnitude limit. Encounters with high-mass stars are potentially more interesting (insofar as they may have been serious Oort cloud perturbers). The Hipparcos database is sufficient to inform us that no high mass star still in existence has encountered the Solar System as closely as Gliese 710 within a few million years of the present. But if projections could be extended for tens of millions of years, some candidates may be found. This would require not only very precise data, but also a precise mass model of the Milky Way because accurate projections must be non-linear on time-scales beyond a few million years.

Thanks to everyone for your interest!
– Erik Anderson

jkittle December 1, 2012 at 12:09

on my Christmas list for my children ages 27 21 annd 15..
Way better than a furby.

James Pailly December 3, 2012 at 3:20

On my Christmas list for myself.

kzb December 3, 2012 at 8:51

One frequently-seen explanation of the Fermi paradox is that interstellar travel is just too difficult: the distances are so great that no intelligent species has ever cracked the problem.

This article highlights an argument against this outlook. One scale-length towards the galactic centre, and the space density of stellar systems is 2.7 times what it is around here. Two scale lengths in and the density is 7.4 times greater. The scale-length of our galaxy is around only 2.1-3kpc according to recent literature.

Intelligent species that evolve in the inner galactic disk will not have the same problem that we have. Over galactic timescales, encounters between stellar systems within 1 light-year will not be uncommon.

I think you can see what I am saying, and I think this is one aspect of the FP discussion that is poorly represented currently.

ljk December 3, 2012 at 12:25

Another great place to hang out in the galaxy is a globular star cluster. We know they have planets and the many stars are very nearby – but despite what it looks like, they are rarely colliding into each other. Whether anyone living there is unaware they are in a globular except once every 2,049 years which freaks them out and causes their civilization to collapse is another matter.

Advanced ETI would find them particularly desirable:

Omega Centauri is probably a galaxy remnant, complete with a black hole at its center, which naturally increases the odds of what I just mentioned (black holes make great energy sources and dump sites for advanced civilizations; in fact using the black hole as a dump is how they get their energy):

I want to make clear: My assumption for finding ETI in globular clusters is based on the idea that the aliens are not necessarily natives to those stars but came there from elsewhere for the abundant resources in such a relatively close spot.

Erik Anderson December 3, 2012 at 12:51

@ jkittle & James Pailly: I hope that Vistas will be a gift that you and your family will treasure for many years!

@ kzb: I give an overview of the Fermi Paradox on page 110 and I didn’t miss your point. It was definitely articulated by Edward Teller, whom I explicitly quote: “…as far as our Galaxy is concerned, we are living somewhere in the sticks, far removed from the metropolitan area of the Galactic center.”

Thanks again.

ljk December 3, 2012 at 12:53

Erik Anderson said on November 30, 2012 at 22:16:

“If anyone can direct me to EXACT information about the escape trajectories of Pioneers 10 & 11 and Voyagers 1 & 2, I could (for fun!) report flyby projections for these spacecraft over the next few million years.”

Erik – First I want congratulate you on your excellent and thought-provoking book. It shall definitely become my holiday present to me.

As for your request regarding where Pioneer 10 and 11 and Voyager 1 and 2 will be in the far future, this Web site provides some good starter information, which I include here after the hyperlink:

42,000 AD

Voyager 1 is passing near the red dwarf star, AC+79 3888

Launched by NASA in 1977, the Voyager I space probe continues to drift through interstellar space. It is now passing near AC+79 3888, an M-type main sequence star in the constellation of Camelopardalis, close to Polaris.* Its sister probe, Voyager 2, will reach Sirius in approximately 298,000 AD.

2,000,000 AD

Pioneer 10 is approaching the Aldebaran system

After travelling at roughly 2.6 AU per year, Pioneer 10 begins to approach the Aldebaran system in 2,000,000 AD.*

4,000,000 AD

Pioneer 11 is approaching the Lambda Aquilae system

After four million years, it passes by Lambda Aquilae, a blue-white B-type main sequence dwarf star, approximately 125 light years from Earth.* Like its sister, Pioneer 11 carries a plaque with a message from humankind.

This site Heavens Above also provides details on the five space probes currently leaving our Sol system:

Erik Anderson December 4, 2012 at 1:06

@ ljk: Glad the book interests you! The information at is no good at all. Aldebaran’s radial velocity alone (54.2 km/s) exceeds Pioneer 10′s heliocentric velocity (12.172 km/s) by a factor of ~4.5. In 2 million years, Pioneer and Aldebaran will be even further apart than they are now! Heavens Above seems to show current spacecraft positions by ~constellation~ as seen from Earth, but I would like to know the ~sky coordinates~ of each spacecraft’s “vanishing point” at arcsecond-precision or better.

ljk December 4, 2012 at 10:52

Erik, I am trying to find more detailed information, but so far what I do have may or may not be useful to you.

There are a few more star passings by the four first interstellar vessels listed here:

Checking the individual entries for the space probes from Wikipedia, there is this addition on Voyager 1, which I quote:

“Voyager 1 is not heading towards any particular star, but in about 40,000 years it will pass within 1.6 light years of the star Gliese 445, which is at present in the constellation Camelopardalis. That star is generally moving towards our Solar System at about 119 km/s (430,000 km/h; 270,000 mph).[33]”

New Horizons may be deflected to another KBO after its flyby of Pluto in 2015, so its final galactic destination may be too early to tell.

Perhaps one of the readers here who are so good with calculations can improve upon what we know about the destinations of our first truly deep space probes. We should know where our first interstellar ambassadors are going for a number of reasons.

Erik Anderson December 4, 2012 at 14:19

Hi again, ljk. My own data indicate that Gl 445 will come to within 3.5 light years of the ~Sun~ 45,000 years from now.

So the projected Voyager 1 encounter (somewhat nearer and sooner) is certainly in the ballpark. Most likely the best way for me to obtain the information I need is to compute myself the hyperbolic trajectory of each spacecraft from their published orbital elements. Time and again I learn that performing one’s own work more often delivers reliable results than placing faith in others’.

Incidentally, wrt globular clusters, these are very ancient objects comprised of stars which lack heavy elements. The planets they host are most likely gas giants–not terrestrial worlds. However, the highly inclined orbits of globular clusters do intersect the Galactic plane twice per circuit, and as they punch through, numerous disk stars get temporarily mixed in with the cluster. Though the odds are long, this could conceivably happen (or could have happened already) to our own Solar System. (Precise projections of globular cluster orbits are not presently possible.)

ljk March 27, 2013 at 1:25

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